Method and apparatus for controlling exhaust gas flow rate

ABSTRACT

An exhaust emissions control system includes a valve in an exhaust stream portion of a mainstream exhaust ahead of an aftertreatment element such as a catalytic converter. The valve controls the amount of exhaust flowing into a hydrocarbon reformer. A bi-directional acoustical air meter in the exhaust stream portion ahead of the reformer measures the velocity of the exhaust stream portion, and a computer determines the amount of combustion needed in the converter at all times, adjusts the amount of hydrocarbon fuel provided to the reformer, and adjusts the position of the valve to provide the optimum amount of exhaust gas flow into the reformer to achieve a desired temperature in the converter.

RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS

The present application draws priority from U.S. Provisional Patent Application Ser. No. 60/606,411, filed Sep. 1, 2004.

TECHNICAL FIELD

The present invention relates to exhaust emissions control systems; more particularly, to means for regulating the flow rate of an exhaust stream from an energy producing source; and most particularly, to method and apparatus for measuring and regulating the flow rate of an exhaust stream for the purpose of controlling emissions.

BACKGROUND OF THE INVENTION

The effort to control exhaust emissions from various energy producing sources has been an ongoing for many years. By way of example, recently, exhaust emissions from a diesel engine have come under intense scrutiny with the advent of stricter regulations, both in the U.S. and abroad. While diesel engines are known to be more economical to run than other internal combustion engines such as spark-ignited engines, diesel engines inherently suffer disadvantages in the area of emissions. For example, in a diesel engine, fuel is injected during the compression stroke, as opposed to during the intake stroke in a spark-ignited engine. As a result, a diesel engine has less time to thoroughly mix the air and fuel before ignition occurs. The consequence is that diesel engine exhaust contains incompletely burned fuel known as particulate matter. It is known to use particulate traps which physically trap the particulates. However, these traps must be repeatedly regenerated by oxidizing the trapped particulates in an efficient and cost effective manner.

Also, it is known in the art that because a diesel engine runs relatively lean (approximately 60:1 air/fuel ratio at idle), nitrogen oxides (NOx) are readily developed in diesel exhaust. There are a number of proposals being considered to reduce these emissions constituents in diesel exhaust. For example, it is known in the art to use NOx adsorbers, in the form of catalysts, as a way of reducing tailpipe NOx by converting it to NO₂. Further, it is known in the art to add hydrocarbon fuel to an exhaust gas stream to assist catalysis by combusting the fuel to raise the temperature of the catalyst bed. Such addition can be wasteful of fuel if the fuel flow rate is not optimized.

What is needed in the art is a means for providing heat to exhaust aftertreatment devices in an efficient and cost effective manner without wasting hydrocarbon fuel.

What is further needed in the art is a means for measuring reliably the flow rate of exhaust gas to improve exhaust emissions, as for example, to optimize catalysis in a diesel engine application.

It is a principal object of the present invention to reliably measure the flow rate of an exhaust stream to improve emissions. Particularly, by way of example, it is an object of the invention to provide metered amounts of hydrogen-containing reformate to a diesel engine catalytic exhaust converter and/or particulate trap derived from the engine's exhaust to increase the rate of catalysis and the efficiency of particulate burn-off therein.

It is a further object of the present invention to reliably and accurately measure and control the flow rate of exhaust gas being diverted to the hydrogen reformer.

SUMMARY OF THE INVENTION

In the example described, an exemplary exhaust gas emissions control system in accordance with the invention includes an aftertreatment element such as a catalytic converter disposed in the exhaust line of an internal combustion engine. A controllable valve in a branched section of the main exhaust gas flow path ahead of the converter distributes a portion of the oxygen-rich exhaust gas flow into a hydrocarbon reformer. Reformate containing H₂ and CO generated by the reformer is directed into the catalytic converter as a fuel source therein to raise the temperature of the converter for more complete combustion and catalytic conversion of the non-reformed exhaust and for more a more efficient regeneration of any particulate trap.

A bi-directional acoustic air meter (BAAM) in the exhaust flow stream ahead of the reformer measures the velocity (and hence volume and mass flow) of the exhaust stream flowing to the reformer. A programmable electronic control means, for example, a computer, determines the amount of combustion needed in the converter at all times, and adjusts the amount of exhaust provided to the reformer by the valve to provide the optimum amount of exhaust gas flow into the reformer to supply reforming oxygen thereto. The BAAM is especially well-suited, over other flow-measuring means, to measuring the exhaust gas flow into the reformer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawing, in which:

FIG. 1 is a schematic diagram, in accordance with the invention, of a system for controlling the amount of diverted exhaust gas flowing to a reformer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a system 10 for enhancing exhaust gas emissions control from an internal combustion engine 12, and especially from a diesel engine, includes a mainstream exhaust flow 16 flowing from engine 12, and a branched second exhaust stream portion 22 of mainstream exhaust flow 16. Valve 14 is disposed in second exhaust stream portion 22. A first exhaust stream portion 18 of mainstream exhaust flow 16 passes through directly to an aftertreatment element 20 containing one or more aftertreatment devices. The aftertreatment element may contain, for example, a NOx adsorber 20 a, a particulate trap 20 b, or an oxygen catalyst 20 c, or any combination thereof. The flow of second exhaust stream portion 22 of mainstream exhaust flow 16 is controlled by valve 14 into a hydrocarbon reformer 24 such as is conventionally known in the art for producing hydrogen and carbon monoxide reformate 26 and heat by the partial oxidation of hydrocarbon contained in second exhaust stream portion 22.

Reformate 26 containing hydrogen and carbon monoxide as fuels, and heat, is produced by reformer 24 and is directed into aftertreatment 20 wherein the reformate is combusted in the presence of oxygen in first portion 18 to elevate the temperature within aftertreatment element 20, thereby beneficially increasing the rate and completeness of catalysis of noxious compounds in first exhaust stream portion 18 and second exhaust stream portion 22. Disposed in second exhaust stream portion 22 of mainstream exhaust flow 16 between valve 14 and reformer 24 is a fluid flow meter 30 for measuring the flow rate of second exhaust portion 22 into reformer 24. Flow meter 30 optionally may be provided as a component of reformer 24, in the inlet thereof. A programmable controller 32, preferably a computer, controls operation of valve 14 by feedback signal 15 and thus the amount of exhaust gas flowing to reformer 24 via an algorithm. Input conditions (for example, temperature) within aftertreatment element 20 are sent 34 to controller 32 which causes the optimal amount of hydrocarbon laden second exhaust stream portion 22 to be sent into reformer 24. Controller 32 may also receive input conditions 28 (for example, flow) from flow meter 30, or input conditions 29 (for example, temperature, time) from reformer 24.

Flow meter 30 is more preferably an acoustical gas flow meter 36 and most preferably a bi-directional acoustical air meter (BAAM) 38, for example as disclosed in U.S. Pat. No. 4,527,433, the relevant disclosure of which is incorporated herein by reference. Such a device includes first and second ultrasonic transducers that measure the apparent sonic velocities when transducing upstream and downstream of the direction of exhaust gas flow and converts the measured sonic velocities into an actual gas velocity. As the cross-sectional area of the conduit through the BAAM and the gas temperature and density are known, the mass flow is readily calculated.

A BAAM is well-suited to such use in comparison with other prior art anemometric devices. A BAAM, in accordance with the invention, may be used to meter an exhaust outlet stream from any exhaust producing energy source including, but not limited to, the outlet stream from a power train reformer, from a fuel cell, from a turbine, or from an internal combustion engine including a spark ignited or a compression ignited internal combustion engine.

An exhaust environment from an energy source, and especially a diesel exhaust, may be extremely demanding and can readily foul and incapacitate other types of anemometers. For example, hot wire or heated film anemometry requires a minimum temperature differential of about 200° C. between the heated sensing elements and ambient air in order to produce sufficient least-bit airflow resolution. These methods can work well at the ambient temperatures of engine air intake systems, but exhaust temperatures of 200° C. to 400° C., such as those found in a diesel exhaust, or 400° C. to 700° C., such as those found in the exhaust of a spark-ignited engine, require the sensing element to operate at temperatures between 400° C. and 900° C. This significant increase in the operating temperature would tend to severely compromise the durability and robustness of conventional hot wire or heated film anemometers.

In pressure-area systems, both the transducers and the sample area, usually a venturi, are vulnerable to particulate contamination and coking associated with diesel exhaust.

In vaned or air-door systems, exhaust temperatures can impact the durability of bearings, and particulates can contaminate and coke up the vane and the flow passages.

Conversely, a BAAM is insensitive to such conditions because the ultrasonic transducers, being in continual vibration, are self-cleaning, and because the acoustic properties of the transducers have relatively low thermal performance sensitivity.

While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims. 

1. A system for aftertreatment of an exhaust gas stream, comprising: a) a valve for controlling a second gas stream portion of said exhaust gas stream; b) an after treatment element disposed in a first gas stream portion of said exhaust gas stream for receiving at least said first gas stream portion; c) a reformer for receiving said second gas stream portion and for reforming hydrocarbon fuel from said second gas stream portion to form a reformate, said reformate being provided into said aftertreatment element; and d) a gas flow meter for controlling the flow of said second gas stream portion into said reformer.
 2. A system in accordance with claim 1 wherein said gas flow meter is an acoustical gas flow meter.
 3. A system in accordance with claim 2 wherein said acoustical flow meter is a bi-directional acoustical gas flow meter.
 4. A system in accordance with claim 1 wherein said gas flow meter is located in said second gas stream portion.
 5. A system in accordance with claim 1 further including a programmable controller.
 6. A system in accordance with claim 5 wherein said programmable controller is a computer.
 7. A system in accordance with claim 1 wherein said aftertreatment element is selected from a group consisting of a NOx adsorber, a particulate trap, and an oxygen catalyst.
 8. A system for reforming hydrocarbon fuel from the exhaust gas stream of an internal combustion engine, comprising: a) a hydrocarbon reformer; and b) a bi-directional acoustical gas flow meter located in said gas stream for controlling the flow of exhaust gas into said reformer.
 9. A system in accordance with claim 8 wherein said engine is selected from the group consisting of spark-ignited and diesel.
 10. An internal combustion engine having a system for catalytically modifying the exhaust gas stream of the engine, said engine comprising: a) a valve for controlling a second gas stream portion of said exhaust gas stream; b) an after treatment element disposed in a first gas stream portion of said exhaust gas stream for receiving at least said first gas stream portion; c) a reformer for receiving said second gas stream portion and for reforming hydrocarbon fuel from said second gas stream portion to form a reformate, said reformate being provided into said aftertreatment element for combustion therein; and d) a gas flow meter for controlling the flow of said second gas stream portion into said reformer.
 11. A system for treatment of an exhaust gas stream, comprising: a) an exhaust producing energy source for producing said exhaust gas stream; and b) a bi-directional acoustical gas flow meter for measuring the flow of said exhaust gas stream.
 12. A system in accordance with claim 11 further including an emission control device disposed in flow communication with said exhaust producing energy source for receiving said exhaust gas stream, wherein said bi-directional acoustical gas flow meter measures the flow of said exhaust gas stream into said emission control device.
 13. A system in accordance with claim 11 wherein said exhaust producing energy source is selected from the group consisting of power train reformer, fuel cell, spark-ignited internal combustion engine and compression-ignited internal combustion engine.
 14. A system in accordance with claim 11 further including a reformer for receiving said exhaust gas stream and for reforming hydrocarbon fuel from said exhaust gas stream, said bi-directional acoustical gas flow meter disposed in flow communication with said reformer for measuring the flow of said exhaust stream into said reformer. 